Vision-dependent changes in the choroidal thickness of macaque monkeys

PURPOSE. TO determine whether changes in the eye's effective refractive sta te produce changes in the thickness of the choroid in infant monkeys. METHODS. Normal developmental changes in choroidal thickness were studied i n 10 normal rhesus monkeys. Hyperopia or myopia was induced by rearing 26 i nfant monkeys with either spectacle or diffuser lenses secured in front of one or both eyes. The treatment lenses were worn continuously beginning at approximately 3 weeks of age for an average of 120 days. Refractive status and ocular axial dimensions, including choroidal thickness, were measured b y retinoscopy and high-frequency A-scan ultrasonography, respectively. RESULTS. Three lines of evidence indicate that the normal increase in choro idal thickness that occurs during early maturation can be altered by the ey e's refractive state. First, in monkeys experiencing form deprivation or th ose in the process of compensating for imposed optical errors, choroidal th ickness and refractive error were significantly correlated with eyes develo ping myopia having thinner choroids than those developing hyperopia. Second . the choroids in eyes recovering from binocularly induced myopia increased in thickness at a faster rate than the choroids in recovering hyperopic ey es. Third, monkeys recovering from induced anisometropias showed interocula r alterations in choroidal thickness that were always in the appropriate di rection to compensate for the anisometropia. These changes in choroidal thi ckness, which were on the order of 50 mu m, occurred quickly and preceded s ignificant changes in overall eye size. CONCLUSIONS. Changes in the eye's effective refractive state produce rapid compensating changes in choroidal thickness. Although these choroidal chang es are small relative to the eye's refractive error, they may play an impor tant role in the visual regulation of axial growth associated with emmetrop ization.